80 Mr. F. W. Edwards on the Old- World 



definitely with the basal plates, and are ventral rather than 

 dorsal to the mesosome. However, if we regard both organs 

 as belonging to the tegminal ring of the genital tube (which 

 seems most probable) there can be no great obligation to 

 using the same name in each case. A name is required for 

 the unpaired median portion. It cannot be called the 

 tegmen, since this term has been used by Sharp and Muir 

 for " the lateral lobes [parameres] and basal piece together/' 

 while in the present case the basal plates are distinct 

 structures. I propose the term dorsal plate, in default of a 

 better; it seems to be the analogue of the ventral plate 

 described by Sharp and Muir in the Scarabseidse, which is 

 also fused with the parameres^ and morphologically on the 

 dorsal side of the tube. 



The basal plates are well developed, and obviously homo- 

 logous with those of the Culicidse. They are usually in the 

 form of two distinct latero- ventral plates, but are sometimes 

 connected in the mid-ventral line by a narrow bridge of 

 chitin ; in one species. (S. semilimpida) this bridge is quite 

 broad. From this condition it is easy to imagine a transition 

 to a state in which the basal plate forms an unpaired ventral 

 piece. In the species mentioned the connecting bridge is 

 external, the mid-ventral portion of the second connecting 

 membrane not being invaginated. 



Distal to the dorsal and basal plates, and connected with 

 them by a short straight membrane, is a complete ring of 

 chitin, generally tubular in form, but varying greatly in 

 length in the different species. Although it is possibly the 

 homologue of the mesosome of the Culicidse, it is certainly 

 not the same as the median lobe of Sharp and Muir, since 

 the membrane connecting it with the dorsal and basal plates 

 is very short and not at all invaginated; it may best be 

 regarded rather as a distal tubular portion of the tegminal 

 ring, such as has been noted by Sharp and Muir in certain 

 Coleoptera. It is the organ called the penis by de Meijere 

 and others, and, though this term is not free from objection, 

 I propose to retain it provisionally ; Snodgrass's term " penis- 

 guard " would be equally appropriate. 



At the tip of the penis is a small circular opening, from 

 which the genital tube is continued backwards as a thin- 

 walled tube (lying within the penis) as far as the base of the 

 penis, or a little fartlier ; it then enlarges again into a 

 chitinous body, which is provided with a conspicuous 

 apodeme extending towards the interior of the body. At the 

 base of this apodeme is a hole in the sac, which probably 

 marks the point at which the membranous portion of the 



